OvmfPkg: disable list length checks in NOOPT and DEBUG builds

In NOOPT and DEBUG builds, if "PcdMaximumLinkedListLength" is nonzero,
then several LIST_ENTRY *node* APIs in BaseLib compare the *full* list
length against the PCD.

This turns the time complexity of node-level APIs from constant to linear,
and that of full-list manipulations from linear to quadratic.

As an example, consider the EFI_SHELL_FILE_INFO list, which is a data
structure that's widely used in the UEFI shell. I randomly extracted 5000
files from "/usr/include" on my laptop, spanning 1095 subdirectories out
of 1538, and then ran "DIR -R" in the UEFI shell on this tree. These are
the wall-clock times:

           PcdMaximumLinkedListLength  PcdMaximumLinkedListLength
           =1,000,000                  =0
           --------------------------  ---------------------------
FAT        4 min 31 s                        18 s
virtio-fs  5 min 13 s                  1 min 33 s

Checking list lengths against an arbitrary maximum (default: 1,000,000)
seems useless even in NOOPT and DEBUG builds, while the cost is
significant; so set the PCD to 0.

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien@xen.org>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Peter Grehan <grehan@freebsd.org>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Rebecca Cran <rebecca@bsdio.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3152
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Message-Id: <20210113085453.10168-10-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

0 files changed, 0 insertions, 0 deletions